Method of making luminescent screens



June 26, 1962 N. A. M LEOD 3,041,228

METHOD OF MAKING LUMINESCENT SCREENS Filed Nov. 26, 1956 2 Sheets-Sheet l :QEFLECT/VE sue/woes 6L ICE Q EEFLECT/V m PHOSPNOQ IMPEEG (v P4472 23 28 wrsA/s/ w/vs Pam? x 2A vs 36 Pm rose/mac I I I We Mann/v4. McLean IN V EN TOR. f2 6' I 3 G/W June 26, 1962 N. A. MacLEoD 3,041,228

METHOD OF MAKING LUMINESCENT SCREENS Filed NOV. 26, 1956 2 Sheets-Sheet 2 Noe/mu 4. Mac Leap INVENTOR.

United States atent 3,641,223 METHOD OF MAKING LIJMINESCENT SCREENS Norman A. MacLeod, Route 2, Box 115, Hornet, Galif, assignor of one-half to I. J. McCullough, Vernon, Calif. Filed Nov. 26, M56, fier. No. 624,378 3 Claims. (Cl. 156-67) This'invention relates to luminescent screens and methods for making the same.

It is an object of this invention to provide an improved screen for receivingexcitation energy and converting it into useful radiant energy in or near the visible spectrum. The received energy may be in the form of moving subatomic particles, such as an electron beam, or may be in the form of-radiant energy, such as X-rays or ultraviolet light.

Zinc sulfide intensifying screens have been used in the past to convert X-rays into radiant energy within a spectrum to which photographic plates are more sensitive. Such zinc sulfide intensifying screens, however, have the limitation that their effect is limited to surface action without appreciable depth of conversion.

It is another object of this invention to overcome this superficial limitation of the prior art Zinc sulfide X-ray intensifying screens.

Optically transparent plastic screens impregnated with luminescent substances, or phosphors, may be used; and up to a point, the thicker the screen, the greater is the intensification, or conversion of received energy to useful radiant energy in or near the visible spectrum. Thickening of the screen is, however, accompanied by loss of definition, or image sharpness.

Another object of this invention is, therefore, to obviate the lack or loss of definition associated with the use of such phosphor impregnated plastic screens.

In accordance with these and other objects which will become apparent hereinafter, preferred forms of the present invention and preferred methods of making the same will now be described with reference to the accompanying drawings, wherein:

FIG. 1 shows an early step in the production of a compartmented screen constructed in accordance with the present invention;

FIG. 2 illustrates a further step in the production of such a screen;

FIG. 3 is a fragmentary enlarged view showing one corner of a screen constructed in accordance with the present invention;

FIG. 4 is a fragmentary cross-section showing a further refinement of the present invention;

FIG. 5 is a fragmentary cross-section showing a still further refinement of the present invention;

FIG. 6 is aframentary perspective view illustrating an alternative form of configuration which the screen compartments may assume;

FIG. 7 is a still further alternative modification of the FIG. 6 style of compartment;

FIG. 8 is a schematic View illustrating an arcuate or curved screen constructed in accordance with the present invention;

FIG. 9 is an enlarged fragmentary view of a portion of FIG. 8;

FIG. 10 is a perspective view showing one element useful in the practice of another form of the present invention;

FIG. 11 is a schematic view illustrating a plurality of elements of the type of FIG. 10 stacked together;

FIG. 12 is a schematic view illustrating schematically a step in the production of a screen as shown in FIG. 10; and

FIG. 13 illustrates a further step in this method of screen production.

along plane-s transverse to the first planes so as to form ice The product of the present invention is a luminescent compartmented screen having a finite but very small thickness ranging from .010 inch to .200 inch in thickness. The screen is interlaced by a multitude of walls transverse or normal to the surface of the screen, which walls form tiny compartments extending normal to the surface of the screen. The interior of the compartments themselves is optically translucent, while the walls of the compartment are optically opaque. Within each compartment is a luminescent substance, or phosphor, having the property of converting particulate energy or short wave length energy into energy lying in or near the visible spectrum, so that the excitation of the screen may be seen by the human eye, or recorded by a photographic emulsion, fluorescent screen photo-multiplier tube or any other photosensitive mechanism.

The screen is preferably made of a translucent substance that is to say, the compartments are filled with the translucent substance, which is preferably a plastic but may be gel, liquid or crystalline. It is preferred to con tain the luminescent substance, or phosphor in the compartments by dispersing it substantially homogeneously throughout the plastic. Both the plastic (as aforesaid) and the phosphor are essentially translucent, so that light is not significantly attenuated in its passage through the compartment.

The compartmentation, effected by use of the opaque walls, produces a sharp definition, which would be absent without the walls, because the energy, upon striking the phosphor-impregnated plastic causes emanation of light waves in all directions, thus losing or destroying definition. By compartmenting as aforesaid, definition is retained, and particularly so if the depth of the compartments, i.e. the thickness of the screen, is made several times the maximum dimension across the compartment. It is preferred to make the depth from 3 to 10 times as great as the width or other maximum cross dimension of the compartment.

While it is preferred to employ the phosphor by dispersing it throughout the plastic in the compartment, the phosphor may also be applied by lining the walls of the compartment therewith. applying the phosphor may be employed to advantage. it 'is preferred to make the walls light reflective, in order to preserve to the maximum the light which is generated in the compartment by the excitation from the particulate beams or the radiant energy.

Screens in accordance with the present invention are particularly useful in the field of X-rays, and in the interest of clarity will be described in that connection. It is to be understood, however, that, as mentioned hereinbefore, any suitable form of excitation may be employed.

Methods of constructing screens in accordance with the present invention will now be described with reference to the drawings.

In FIG. 1 there is shown an orthogonalbody 21 of translucent plastic, which in its production has been impregnated with a translucent phosphor dispersed substantially homogeneously throughout the body of the plastic 21. The body 21 is first sliced into a plurality of thin slices 22. Between the slices there is placed an opaque coating. This may be done by coating either one or both sides of each slice with a material which forms a reflective surface, as well as being opaque, as for example, magnesium oxide. A layer or coating of bonding material is then applied between each of the slices, and the body 21 is reformed by bonding the slices back together again. If desired the opaque material may be incorporated in the border to minimize steps. The body 21 is now in effect optically laminated by the opaque walls formed from the coating material.

The body 21 is then sliced into a plurality of slices If desired, both methods of another series of slices transverse to the first formed slices. The coating-bonding operation is then repeated, and the body 21 is reformed into the doubly laminated body shown in FIG. 2. This body thus has a plurality of tubular optical compartments, each tube consisting of a square ranging on the side from about .003 inch to about .050 inch.

Finally, the body 21 shown in FIG. 2 is sliced along parallel planes normal or transverse to both laminations, to form a plurality of compartmented screens, one corner of such a multi-cellular screen being shown enlarged in FIG. 3. As indicated hereinbefore, the thickness of the screen is preferably from 3 to times as great as the side of one of the compartment squares.

As indicated hereinafter, phosphors may also be embodied in the opaque coating material which forms the compartment walls, thereby to enhance the transmuting effect and give greater light conversion within the screen.

A typical use of a screen constructed as aforesaid and as illustrated in FIGS. 1, 2 and 3 is illustrated in FIG. 4.

In this instance, one face of the screen is provided with an intensifying plate, preferably in the form of a reflective, opaque coating 23. Contiguous to the opposite face or surface of the screen there is laid a photographic negative 24. X-rays applied to the screen from above, as shown at 26, pass through the photographic film or plate 24 where they have some effect, since the film has some sensitivity to X-rays. The rays 26 pass into the individual compartments 27, as shown at 28, and there are converted by the phosphor into radiant energy lying in the visible or near visible spectrum to which the film is much more sensitive. These light rays emanate, and are reflected, upward, back to the plate or film 24. The presence of the walls 29 between compartments 27 pref vents the light rays from being dispersed horizontally along the screen and film 24, and thus sharp definition is preserved, the degree of definition varying inversely with the size or cross-section of the compartments 27. The appreciable depth or thickness of the screen compared to the cross-section of each compartment 27 allows for maximum practical conversion of the X-ray energy into visible light as the X-rays penetrate deeper and deeper into the compartment 27. Up to an optimum point, intensification varies directly with the thickness of the screen.

To further trap the light, and thereby increase intensification, the upper surface of plate 24 may be coated with a thin layer of material which is light reflective but otters little attenuation to passage of X-rays or particulate beams.

A further refinement in this use of the invention is illustrated in FIG. 5, wherein electrically conductive films or plates 31 and 32 are applied, as by coating, to each surface of the screen, and an electric potential is applied between the two plates, by means of the terminals 33 and 34. The presence of the electrostatic field across the compartments 27 containing the phosphor enhances the photo-emission, and gives increased conversion of X-ray energy into visible light. In this application of the present invention, at least the film 32 must be relatively translucent as well as conductive in order to allow the light genera-ted within the compartment to pass back and affect the photographic film 36. The opposite side or surface of the screen, however, is preferably opaque, and this may be conveniently effected by providing a reflective screen 37 in the same manner as the screen or plate 23 was provided in FIG. 4.

Another manner of providing the compartments in the screen is illustrated in FIG. 6. In this form of the invention, a plurality of corrugated sheets of phosphorimpregnated plastic 38 are formed, preferably by extrusion, and are then interlocked one with the other and bonded together to form the compartments 39. Prior to interlocking, the sheets are coated with an opaque, and

preferably reflective, material as described hereinbefore in connection with FIGS. 1 and 2.

The corrugations of the sheets 38 are preferably offset, 7

as shown particularly in FIG. 6, so that adjacent compartments, for example, compartments 39* and 41 are joined together by narrow isthmus-like passages 42, which minimize the passage of light from one compartment to another, while still retaining physical continuity from compartment to compartment, thus allowing the sheet 38 to be formed or extruded as an integral piece. The opposite corrugated surfaces of the sheet 38 are preferably so formed that the innermost apex of the V on one side. of the sheet 38, as shown at 43, extends slightly beyond the corresponding V apex 44 on the opposite side of the sheet, so that there is effectively blocked a straightthrough line of light passage along the length of the sheet 38. Thus, while there will be some light leakage between adjacent compartments, there is not formed a continuous straight band of light completely across the screen paralleling the sheet 38.

A modification of the sheet shown in FIG. 6 is shown in FIG. 7, wherein the corrugations, instead of having sharp corners, are rounded, as shown at 46 and 47. The coating, bonding, and nesting o interlock-ing are effected in the same manner as the FIG. 6 modification. It will be noted that, as in FIG. 6, the inward extensions of the corrugations overlap in order to preclude passage of a light beam completely along the sheet 48.

If desired, the screen may be made curved, following, for example, the arc of a cylinder or a sphere, as shown schematically in FIG. 8. Such a configuration would be useful where there is essentially a line or point source of excitation as shown at 51. Such sources are to be found, by way of example, in cathode-ray tubes, television screens, and the like. By virtue of the compartmentation shown at 52, definition is greatly enhanced and the impregnation of the plastic compartments 53 with a translucent phosphor gives improved transmutation of the electron beam into visible light energy.

'In FIGS. 10-13, there is shown schematically another method of producing screens in accordance with the present invention. In this instance, the screen compartments are hexagonal in cross-section #as shown in FIG. 12.

This method comprises coating, with an opaque and preferably reflecting film, a plurality of substantially circular cylindrical filaments, shown at 54 in FIG. 10. These filaments are made of plastic, impregnated with phosphor as with the embodiments previously described. A bonding substance is applied to the filaments which are then sheavcd together in contiguous parallel relation as shown in FIG. 10. The geometry of the bundle is such that each cylinder has contiguously therearound 6 other cylinders, as shown in FIG. 11.

The sheaf thus formed is subjected to high pressure from all sides, as shown schematically by the arrows 56. This may be accompanied .by a heating operation, if desired, as when dealing with thermo-plastics. This pres sure (and temperature) is sufficient to deform the plastic and eliminate the interstices 57 between contiguous cylinders. The result is that the circular cylinders are reformed into hexagonal prisms or cylinders as shown in FIG. 12, and retained together by the bonding substance. After the plastic has cooled and the bond has fully set, the sheaf is sliced along planes normal to the axes of the cylinders to form a plurality of compartmented screens generally similar to the screen of FIG. 2., except that they are hexagonal in cross-section instead of square, as mentioned hereinbefore.

While the instant invention has been shown and described herein in what is conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein, but is to be accorded the full scope of the claims.

What is claimed is:

screens comprising: forming a plurality of laminations having corrugated face surfaces and wherein at least some of said laminations are formed of luminescent material, applying an opaque coating to the 'fiaces of said laminations, stacking said laminations with said corrugations in interfitting engagement, said coating forming an Opaque Wall between adjacent laminations, and slicing said laminations along parallel planes perpendicular to said corrugations to form a member having a plurality of compartmented screens.

2. A method of making luminescent compartmented screens comprising; forming a plurality :of laminations of luminescent material in which the side surfaces thereof have corrugated configurations which interfit with confronting corrugations with complete surface engagement when said laminations are stacked each on the other; applying an opaque coating on said side surfaces, stacking said laminations in interfiitting fiace-to-fiace engagement, said coating forming an opaque wall between adjacent laminations; and slicing said stacked l aminations along parallel planes perpendicular to the side surfaces thereof to form a member having a plurality of compartmented screens.

3. A method of making luminescent compaitmented screens according to claim}, wherein the corrugated confignations on opposite side surfaces of said laminations are oriented to form cross-sectional areas of difiierentthicknesses between said surfaces;

602,159 Harrison Apr. 12, 1898 1,883,290 Ives Oct. 18, 1932 1,883,291 Ives Oct. 18, 1932 2,053,173 Astima Sept. 1, 1936 2,122,246 *Clewell June 28, 1938 2,360,516 Sehmidl-ing Oct. 17, 1944 2,372,359 Cook Mar. 27, 1945 2,527,752 May Oct. 31, 1950 2,648,013 Smith Aug. 4, 1953 2,659,679 Koller Nov. 17, 1953 2,682,478 Howse June 29, 1954 2,690,979 Law Oct. 5, 1954 2,835,822 Williams May 20, 1958 2,882,413 Vingerhoets Apr. 14, 1959 

1. METHOD OF MAKING LUMINESCENT COMPARTMENTED SCREENS COMPRISING: FORMING A PLURALITY OF LAMINATIONS HAVING CORRUGATED FACE SURFACES ANDWHEREIN AT LEAST SOME OF SAID LAMINATIONS ARE FORMED OF LUMINESCENT MATERIAL, APPLYING AN OPAQUE COATING TO THE FACES OF SAID LAMINATIONS, STACKING SAID LAMINATIONS WITH SAID CORRUGATIONS IN INTERFITTING ENGAGEMENT, SAID COATING FORMING AN OPAQUE WALL BETWEEN ADJACENT LAMINATIONS, AND SLICING SAID LAMINATIONS ALONG PARALLEL PLANES PERPENDICULAR TO SAID CORRUGATIONS TO FORM A MEMBER HAVING A PLURALITY OF COMPARTMENTED SCREENS. 